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General Tech HS6 Carburetor Bushings

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KVH

KVH

Obi Wan
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Has anyone used a small lathe to drill out old SU carb bushings and press in new ones? If so, how did you secure the carb body to the tail stock—so it was square and firm in place?
 
I used a drill press with a machine vice to hold the carb body.

If I were doing it in a lathe, I would first try to hold the carb body in a 4 jaw chuck, and use the drill/reamer on the tail stock chuck. You can use the chuck with a rod through the carb throttle bore to align the body on the 4-jaw.
 
It looks like they did it by hand...which will work fine if you have a steady hand and don't rush it.

In a lathe, I would mount the carb body to the spinning 4-jaw chuck. 2 opposing teeth on the machined carb inlet/outlets, and the other 2 teth as necessary on the rounded outside of the carb body. Use a drill type chuck in the tail stock, and use a rod in the chuck to help center the tail chuck to the throttle shaft bore. Then spin the carb and, using a drill in the tailstock, drill and final ream the carb bore. You will not need your carriage tool holder at all for this operation.
 
Does the drill bit accomplish the reaming, or is a reaming tool then needed as well. Also, do you know whether the new bushes, which I believe are 3/8 inch, will press cleanly into the carb sleeves, or is that where more reaming may be needed?
 
Normally, you would drill with a 23/64 drill, and follow with a 3/8" reamer. The 6 flute reamer is much more accurate than a 2 flute drill bit. If you have ever closely watched a 2 flute drill, it creates a hole with 3 wallows in the hole, by it's nature. The 6 flutes of a reamer remains centered for a near perfectly round hole. Of course, if you only have a 3/8" drill bit, you can get by with that.
 
You would probable need a straight flute reamer. Known as a chucking reamer. Unlike a hand reamer which is tapered over the first section the chucking reamer is parallel.

David
www.mcmaster.com

McMaster-Carr

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I saw one clever technique where the guy pulled a long reamer backwards through the body, using the shaft of the reamer for alignment. In that case, no need for even a drill press. Not every reamer can be used that way, though.

(Edit: I just noticed your link, above. That may be what I'm remembering.)

If I were doing this again, I'd blow for a good reamer that was long enough to go through both bushings simultaneously. Then I would make bushings with a slightly undersized ID, press them into the body, and finally ream them to the right ID.
 
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My experience rebuilding 4 sets of HS6 carbs is that the butterfly shafts took the wear rather than the carb body. This is different from the H6 carbs due to a very different linkage setup. I would suggest that you fit a new set of shafts into the carb bodies and then determine if you need to ream and bush the bodies.
Charley
 
That’s what I plan to do, first check play with new shafts. From what I now see, the worn shafts appear to account for about 2/3rds of the play. I can see that the old bushes suffered some of the mutual wear. But maybe acceptable. Once the new shafts and butterflies are in I’ll sure be reluctant to rethink it all. So it’ll be a judgment call.

(See the price of that oversize reamer Moss offers? Sheesh. My goal wouldn’t be to oversize in any case)

But about reamers, why not order a 7 inch one with 1.75 spiral flute and work backward as the write-up shows? Seems right. The ones I found have a shaft just under 5/16 ID and that may work. Not sure why the Moss bushings weren’t used. He ordered his from MMC.
 
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